Seismic Bracing at Extended Lengths

[bmlxd40]

I have a retrofit project that requires seismic bracing. The unique situation here is that the concrete structure is 18 feet above the ceiling. If possible, I want to prevent running the main and lines up high.

I'm not sure as to the best way to brace this system when the pipe is installed near the existing ceiling. When we use the cable restraints for the branchlines, the cables will have to be so long that there will be considerable sag in the cable. If the cable is pulled tight at those long lengths, it picks the pipe up out of the hangers.

The rigid bracing on the mains could easily exceed 25 feet in length. Obviously, this presents it's own set of problems.

Has anyone encountered this before, or know of a possible solution?? We must maintain a UL listing and FM approval on the final assembly.

Thanks in advance.

 

[TravisMack]

Unfortunately, as seismic bracing is becoming a more defined and calculated aspect of fire sprinkler systems, it can significantly influence the layout of the system. We used to run low with short drops and long hangers because rod is much cheaper than pipe. Well, that is not always possible when seismic conditions come in to play. You could use 2" pipe for your bracing and calc the braces with your l/r value of 300. This would allow you a maximum length of brace pipe of 19'-8". If you are at the 45° angle for bracing, that would give you about 8' down from the deck and about 10' above the ceiling. Not ideal, but that is really about the best you are going to get without using cable bracing. You will still likely need cable for your branch line restraint.

Good luck on the project.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[bmlxd40]

Thanks, I was afraid that would be the answer I received. It appears that we will be running the pipe up high.We suspected that was the case from the beginning, but we figured it was worth a shot to look for alternatives.

I cant help but think about the long drops though. During a seismic event, wouldn't this become an issue??

 

[TravisMack]

Also, depending on the ceiling construction, you will need to either have large holes in the ceiling for the drops, or you need to use flexible hose sprinkler adapters - Flexhead, AquaPex, etc...

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com